Singleton Design Pattern

Singleton Design Pattern

There are some instances in the application where we have to use just one instance of a particular class.

Singleton pattern is one of the simplest design patterns in Java, which comes under creational pattern.

Important :

* Ensure unique instance by defining class final to prevent cloning.

* May be extensible by the subclass by defining subclass final.

* Make a method or a variable public or/and static.

* Access to the instance by the way you provided.

* Well control the instantiation of a class.

* Define one value shared by all instances by making it static.

Example :

1. DisplayCurrencyFormat.java

package DesignPatterns.Singleton;

import java.text.DecimalFormat;

public class DisplayCurrencyFormat {

     private static DisplayCurrencyFormat currencyFormatuniqueInstance;

     private boolean ENABLE_ROUNDING = false;

     private boolean ENABLE_DECIMAL = false;

     private boolean ENABLE_GROUPING = false;

     private String ROUNDING_TYPE = "abs";

     public static synchronized DisplayCurrencyFormat getInstance(){

           if(null == currencyFormatuniqueInstance){

                 return currencyFormatuniqueInstance = new DisplayCurrencyFormat();

           }

           return null;

    }

    public String setDisplayFormat(double value){

           if(currencyFormatuniqueInstance.isENABLE_ROUNDING()){

                 if("ceil".equalsIgnoreCase(currencyFormatuniqueInstance.

getROUNDING_TYPE())){

                        value = Math.ceil(value);

                 }

                 if("floor".equalsIgnoreCase(currencyFormatuniqueInstance.

getROUNDING_TYPE())){

                       value = Math.floor(value);

                 }

                 if("abs".equalsIgnoreCase(currencyFormatuniqueInstance.

getROUNDING_TYPE())){

                       value = Math.abs(value);

                }

          }

          String retValue;

          if(currencyFormatuniqueInstance.isENABLE_DECIMAL() && currencyFormatuniqueInstance.isENABLE_GROUPING()){

                 DecimalFormat df1 = new DecimalFormat( "#,###,###,##0.00" );

                 retValue = df1.format(value);

          }else{

                 if(currencyFormatuniqueInstance.isENABLE_DECIMAL()){

                        DecimalFormat df2 = new DecimalFormat( "#####0.00" );

                        retValue = df2.format(value);

                }else

                if(currencyFormatuniqueInstance.isENABLE_GROUPING()){

                        DecimalFormat df3 = new DecimalFormat( "#,###,###,##0" );

                        retValue = df3.format(value);

                }else{

                        retValue = String.valueOf(value);

                }

         }

         System.out.println("value | retValue --> " + value + " | " + retValue);

         return retValue;

   }

   public boolean isENABLE_ROUNDING() {

         return ENABLE_ROUNDING;

   }

   public void setENABLE_ROUNDING(boolean eNABLE_ROUNDING) {

         ENABLE_ROUNDING = eNABLE_ROUNDING;

   }

   public boolean isENABLE_DECIMAL() {

         return ENABLE_DECIMAL;

   }

   public void setENABLE_DECIMAL(boolean eNABLE_DECIMAL) {

         ENABLE_DECIMAL = eNABLE_DECIMAL;

   }

   public boolean isENABLE_GROUPING() {

         return ENABLE_GROUPING;

   }

   public void setENABLE_GROUPING(boolean eNABLE_GROUPING) {

          ENABLE_GROUPING = eNABLE_GROUPING;

   }

   public String getROUNDING_TYPE() {

          return ROUNDING_TYPE;

   }

   public void setROUNDING_TYPE(String rOUNDING_TYPE) {

          ROUNDING_TYPE = rOUNDING_TYPE;

   }

}

2. SingletonDemo.java

package DesignPatterns.Singleton;

public class SingletonDemo {

      /**

      * @param args

      */

      public static void main(String[] args) {

              SingletonDemo demo = new SingletonDemo();

              demo.execute();

      }

      private void execute(){

              DisplayCurrencyFormat currencyFormatObj = DisplayCurrencyFormat.getInstance();

              currencyFormatObj.setENABLE_ROUNDING(true);

              currencyFormatObj.setENABLE_DECIMAL(true);

              currencyFormatObj.setENABLE_GROUPING(true);

              currencyFormatObj.setROUNDING_TYPE("abs");

              currencyFormatObj.setDisplayFormat(10189.4);

      }

}

Output :

value | retValue [R-t|D-t|G-t]--> 10189.4 | 10,189.40

value | retValue [R-t|D-t|G-f]--> 10189.4 | 10189.40

value | retValue [R-t|D-f|G-t]--> 10189.4 | 10,189

value | retValue [R-t|D-f|G-f]--> 10189.4 | 10189.4

value | retValue [R-f|D-t|G-t]--> 10189.4 | 10,189.40

value | retValue [R-f|D-t|G-f]--> 10189.4 | 10189.40

value | retValue [R-f|D-f|G-t]--> 10189.4 | 10,189

value | retValue [R-f|D-f|G-f]--> 1189.4 | 10189.4